JDBC Problems in programming

    1. take SQL The statement is hard coded to Java Code , Not conducive to system maintenance .
        Imagine how to solve ： take SQL Extracted separately , In profile （xml The way 、properties file ） To configure .
    2. Database connections cannot be reused , It's a waste of database resources .
        Imagine how to solve ： Use the database connection pool to manage database connections .
    3. towards Statement When setting parameters , The position of the parameter is hard coded , Not conducive to system maintenance .
        Imagine how to solve ： Whether it can automatically transfer Java Object to Statement.
    4. Traversal result set ,resultSet.getString Hard code specifies the column name .
        Imagine how to solve ： Can I automatically SQL The query result set is transformed into Java object .

MyBatis Introduce

        MyBatis This is a apache An open source project of iBatis,2010 This project was initiated by apache software foundation Migrate to google code, And renamed it MyBatis.
        MyBatis Is an excellent persistence layer framework , It's right JDBC To encapsulate the process of database operation , Let the developer only need to pay attention SQL In itself , Instead of having to deal with things like registered drivers 、 establish connection、 establish statement、 Manual setting of parameters 、 Result set retrieval, etc JDBC Complex process code .
        MyBatis adopt xml Or primary key will be executed statement Configure it , And pass Java Objects and statement Medium SQL Map to generate the final execution SQL sentence , Finally by MyBatis Framework implementation SQL And map the result to Java Object and return .
        MyBatis It's an incomplete ORM frame ,MyBatis You can also do object relational mapping , But it still needs to be written manually SQL sentence .Hibernate Yes JDBC The package is deep , It's a completely excellent ORM frame , It's fully realized Java Object to Relation Mapping ,SQL No need to write it manually .

Mybatis frame

    Mybatis To configure
    

    1. SqlMapConfig.xml yes MyBatis Core profile for , Configured data source （ Connection pool ）、 Business mapper.xml yes MyBatis Map file of .
    2. SqlSessionFactory Conversational factory , User production session SqlSession.
    3. SqlSession conversation , It's a user oriented facade interface , For operating the database （CRUD）
    4. Executor actuator ,SqlSession Through internal Executor Operating the database ,Executor Need to use Mapped Statement To manipulate the database by encapsulating data information in .
    5. Mapped Statement yes MyBatis An underlying encapsulation object , Encapsulates the SQL sentence 、 Pass in SQL Parameters of statement , take SQL The query results are mapped to Java object .

Mybatis Entry procedure

    1. add to jar package Download address ： link ： http://pan.baidu.com/s/1mgtFYxa  password ：vq10 （ Including source code ）
        The core jar Bag is ：mybatis-3.2.8.jar
        rely on jar Wrapped in lib Under the table of contents
        You also need to add your own database jar package
        Create a Java Project （ The following is the final project diagram ）
        
    2. log4j.properties Log files （ Primary user console printing log）
        add to Source Folder :config, And create log4j.properties
        Use the official website configuration directly , Just change it to DEBUG Pattern     
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log4j.rootLogger=DEBUG, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

    3. establish SqlMapConfig.xml The configuration file
        stay config Create under folder SqlMapConfig.xml
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<? xml  version = "1.0"  encoding = "UTF-8"  ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
< configuration >
     <!--  and spring After integration environments Configuration will be abolished  -->
     < environments  default = "development" >
         < environment  id = "development" >
             < transactionManager  type = "JDBC"  />
             < dataSource  type = "POOLED" >
                 < property  name = "driver"  value = "com.mysql.jdbc.Driver"  />
                 < property  name = "url"
                     value = "jdbc:mysql://localhost:3306/mybatis?characterEncoding=utf8"  />
                 < property  name = "username"  value = "root"  />
                 < property  name = "password"  value = "root"  />
             </ dataSource >
         </ environment >
     </ environments >
 
</ configuration >

    4. establish po class ,User stay package com.hqu.model Next , And create database and corresponding table to insert test data
        The goal is ： take sql The query results are mapped to Java object ,po Class and user Table fields correspond to
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package  com.hqu.model;
 
import  java.sql.Date;
 
public  class  User {
     private  int  id;
     private  String username;
     private  String sex;
     private  Date birthday;
     private  String address;
     private  String detail;
     private  float  score;
 
     // getter and setter .. 
}

    5. To write User.xml（mapper.xml file ） stay config Create folder sqlmap And create User.xml

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<? xml  version = "1.0"  encoding = "UTF-8"  ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
< mapper  namespace = "test" >
 
     <!--  Query user information
     select : take select The tag content is called statement
     id： Is in user.xml Unique identification of ,statement Of id
     parmeterType: Point to sql（ towards statement in ） The type of the parameter passed in
     #{}： Represents a dot ,{} Medium id Represents the name of the incoming variable , When a single value is passed in {} The variables in can be arbitrary
     resultType： take sql The query result set maps to java Type of object  -->
     < select  id = "findUserByName"  parameterType = "string"  resultType = "com.hqu.model.User" >
         select * from User where username = #{id}
     </ select >
 
     < insert  id = "insertUser"  parameterType = "com.hqu.model.User" >
         insert into
         user(username,birthday,sex,address,detail,score)
         values (#{username},#{birthday},#{sex},#{address},#{detail},#{score})
     </ insert >
</ mapper >

6. take User.xml stay SqlMapConfig.xml To configure

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< configuration >
     ...
     <!--  Load mapping file  -->
     < mappers >
         < mapper  resource = "sqlmap/User.xml"  />
     </ mappers >
</ configuration >
7. Mybatis Inquiry procedure
    New class test
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public  class  MybatisTest {
 
     SqlSession sqlSession =  null ;
 
     @Before
     public  void  before()  throws  IOException {
     
         String resource =  "SqlMapConfig.xml" ;  // mybatis Configuration file for
 
         InputStream is = Resources.getResourceAsStream(resource);
 
         //  Create a session factory
         SqlSessionFactory sqlSessionFactory =  new  SqlSessionFactoryBuilder().build(is);
 
         sqlSession = sqlSessionFactory.openSession();  //  From in the conversation factory to conversation
     }
 
     @After
     public  void  after() {
         sqlSession.close();  //  Release resources
     }
 
     @Test
     public  void  testSelect() {
         //  adopt sqlSession Operating the database
         //  The first parameter ：user.xml Defined statement Of id
         //  The second parameter ： Input parameters
         User user = sqlSession.selectOne( "test.findUserByName" ,  "jerome" );
         System.out.println(user);
     }
     
     @Test
     public  void  testInsert() {
 
         User user =  new  User();
         user.setUsername( "jelly" );
         user.setSex( " Woman " );
         user.setAddress( " Shenzhen " );
         user.setScore(12f);
 
         sqlSession.insert( "test.insertUser" , user);
         
         sqlSession.commit();  //  Commit transaction
     }
 
}
end .
code link ： http://pan.baidu.com/s/1sjlzpAP  password ：exmy

Mybatis Is how to solve JDBC The problem of

    1. take SQL The statement is hard coded to Java Code , Not conducive to system maintenance .
        Imagine how to solve ： take SQL Extracted separately , In profile （xml The way 、properties file ） To configure .
        stay mybatis Map file of （ Such as ：User.xml） To configure sql sentence .
    2. Database connections cannot be reused , It's a waste of database resources .
        Imagine how to solve ： Use the database connection pool to manage database connections .
        stay SqlMapConfig.xml Under the environments Node is configured with connection pool
    3. towards Statement When setting parameters , The position of the parameter is hard coded , Not conducive to system maintenance .（ Such as preparedStatement.setString(1,"jerome")）
        Imagine how to solve ： Whether it can automatically transfer Java Object to Statement.
          stay User.xml Pass through paramenterType, Type of input parameter , stay sql Statement passing #｛｝ Represents a space occupying symbol ,｛｝ Is written po The property name , Finish automatically will java Object to sql In the sentence .
    4. Traversal result set ,resultSet.getString Hard code specifies the column name .（ Such as ：resultSet.getString("id")）
        Imagine how to solve ： Can I automatically SQL The query result set is transformed into Java object
        User user = sqlSession.selectOne("test.findUserByName", "jerome");

Refer to the podcast open class ： link ： http://pan.baidu.com/s/1bnbH2qj  password ：9f30
Later detailed in-depth video   link ：http://pan.baidu.com/s/1qWFTzQ0 password ：jqqx （ That's all the information for the time being ）
Reference documents ：
1. http://mybatis.org/mybatis-3/zh/index.html （MyBatis Official documents ）
Corresponding pdf（ english ）： link ：http://pan.baidu.com/s/1pJrL42v password ：2yq0
Corresponding pdf（ chinese ）： link ：http://pan.baidu.com/s/1pJqzBDp password ：dwhf

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